Question

Is there anything built into the core C# libraries that can give me an immutable Dictionary?

Something along the lines of Java’s:

Collections.unmodifiableMap(myMap); 

And just to clarify, I am not looking to stop the keys / values themselves from being changed, just the structure of the Dictionary. I want something that fails fast and loud if any of IDictionary’s mutator methods are called (Add, Remove, Clear).

Answer 1

No, but a wrapper is rather trivial:

public class ReadOnlyDictionary<TKey, TValue> : IDictionary<TKey, TValue> {     IDictionary<TKey, TValue> _dict;      public ReadOnlyDictionary(IDictionary<TKey, TValue> backingDict)     {         _dict = backingDict;     }      public void Add(TKey key, TValue value)     {         throw new InvalidOperationException();     }      public bool ContainsKey(TKey key)     {         return _dict.ContainsKey(key);     }      public ICollection<TKey> Keys     {         get { return _dict.Keys; }     }      public bool Remove(TKey key)     {         throw new InvalidOperationException();     }      public bool TryGetValue(TKey key, out TValue value)     {         return _dict.TryGetValue(key, out value);     }      public ICollection<TValue> Values     {         get { return _dict.Values; }     }      public TValue this[TKey key]     {         get { return _dict[key]; }         set { throw new InvalidOperationException(); }     }      public void Add(KeyValuePair<TKey, TValue> item)     {         throw new InvalidOperationException();     }      public void Clear()     {         throw new InvalidOperationException();     }      public bool Contains(KeyValuePair<TKey, TValue> item)     {         return _dict.Contains(item);     }      public void CopyTo(KeyValuePair<TKey, TValue>[] array, int arrayIndex)     {         _dict.CopyTo(array, arrayIndex);     }      public int Count     {         get { return _dict.Count; }     }      public bool IsReadOnly     {         get { return true; }     }      public bool Remove(KeyValuePair<TKey, TValue> item)     {         throw new InvalidOperationException();     }      public IEnumerator<KeyValuePair<TKey, TValue>> GetEnumerator()     {         return _dict.GetEnumerator();     }      System.Collections.IEnumerator             System.Collections.IEnumerable.GetEnumerator()     {         return ((System.Collections.IEnumerable)_dict).GetEnumerator();     } } 

Obviously, you can change the this[] setter above if you want to allow modifying values.